Process control and monitoring can be advantageous for an array of manufacturing processes, such as advanced adhesive bonding of primary aircraft structural elements. For example, the final strength of a bonded joint for an aircraft structural component may depend upon the proper completion of a number of steps that make up the bonding process. To ensure that adhesive bonded aircraft components are safe to use on commercial transport aircraft, a certification methodology to verify that proper process control and monitoring is being used in adhesive bonding of those aircraft components is needed. Likewise, bonding of a coating or paint to a substrate can depend upon the proper completion of a number of steps that make up the bonding process.
One specific risk to the strength of adhesive bonds is the presence of contaminants, such as silicones, oils, greases, etc., on the surfaces during bonding. One such group of contaminants is silicones, which have been identified as the most detrimental surface contaminates leading to weak adhesive bonds even at exceptionally low concentrations. Unfortunately, silicone coatings are widely used in composite and metal processing of parts for aircraft, for example as mold release agents. As such, silicone residue is often left behind on aircraft parts that need to be adhesively joined. There is a significant need to remove silicone contaminants from fabricated part surfaces while simultaneously providing a surface ready for adhesive bonding in a reproducible, reliable, and automatable manner. There is also a need to be able to detect exceptionally low levels of silicone contaminants known to cause bonding problems (e.g., less than 2 micrograms/cm2), in a manner that is rapid, that is straight forward, that can be used in ambient environments, and that does not require special sample preparation techniques.